1. Field of the Invention
The present invention relates generally to thermal detection systems that detect the failure of mechanical devices when a predetermined temperature has been reached. More particularly, the present invention relates to thermal warning device in a wheel assembly of a railway car to indicate when the temperature of the wheel assembly has reached a level indicative of potential bearing failure.
2. Description of the Prior Art
Various warning devices are used to detect impending trouble in a wheel assembly of a railway car before the actual occurrence of a bearing failure. One indicator of possible bearing failure is the detection of excessively high temperatures in the wheel assembly. In particular, overheating of the wheel assembly may lead to an undesirable incident, such as a train derailment. To forestall such an event, a thermal warning device may be positioned in a wheel assembly to indicate a possible bearing failure when the wheel assembly has exceeded a predetermined threshold temperature.
It is known that thermal warning devices in the form of specially adapted bolts may be substituted for standard bolts that are normally secured to the wheel assembly. These specially adapted bolts or thermal warning bolts determine when a railway car bearing has reached a predetermined threshold temperature, and, as a consequence, provide a warning signal to a wayside station or train crew in time to prevent potential problems. For example, U.S. Pat. No. 4,812,826 to Kaufman et at, which issued on Mar. 14, 1989, provides a thermal warning bolt having the dimensions of a standard bolt and includes a communication circuit for producing a radio frequency signal that provides a warning signal. Responsive to the rise in temperature in the wheel assembly, an antenna, which is positioned axially in the bolt, extends through the head of the bolt. The movement of the antenna triggers the communication circuit to emit the radio frequency signal and, thus, alert a train crew of a possible problem with the wheel assembly.
One problem with implementing a communication circuit in a standard bolt is the sensitivity of its electronic components to heat. The temperature of the wheel assembly can reach levels as high as 250 degrees to 350 degrees Celsius. In order to function properly and reliably, such electronic components require a way to dissipate heat and avoid high temperature levels. Accordingly, high temperatures produced by bearing assemblies may cause communication circuits of thermal warning bolts to malfunction.
Another problem is the mechanical degradation of the bolt due to hollowing the bolt to accommodate the communication circuit. An additional problem is the such bolt may be used only once since the communication circuit in the bolt only transmits when a predetermined threshold temperature is breached. Due to its one shot nature, there is no way to self-test the communication circuit to determine whether it is functional.
In view of the above problem, thermal warning devices have been designed to minimize the adverse effects caused to the thermal sensors' electronic components by exposure to high temperatures. For example, U.S. Pat. No. 5,438,322 to J. M. Martin, et al., which issued on Aug. 1, 1995, provides a thermal warning bolt having a communication circuit positioned in the head of a bolt and a temperature sensor situated at the opposite end of the bolt. The communication circuit is positioned away from high temperatures while the temperature sensor is situated near the wheel assembly. Similar to U.S. Pat. No. 4,812,826 cited above, this thermal warning bolt suffers from the problems of mechanical degradation of the bolt and one shot operation which prohibits self-testing.
In addition, U.S. patent application Ser. No. 08/276,845 to J. M. Denny, et at., which was filed on Jul. 18, 1994 now abandoned, provides a thermal warning device having a temperature sensor situated in a bolt whereas a communication circuit coupled to the temperature sensor is positioned outside of the bolt. In particular, the communication circuit is enclosed in a housing that is situated adjacent to the wheel assembly. The communication circuit of the thermal warning device is positioned away from high temperatures generated by the wheel assembly while the temperature sensor is situated near the wheel assembly for accurate detection of high temperatures. However, similar to U.S. Pat. Nos. 4,812,826 and 5,438,322 cited above, this thermal warning device has the problem of mechanical degradation of the bolt.
Thermal warning devices that provide reliable detection of high temperatures are typically expensive and require extensive assembly and installation. In order to obtain an accurate high temperature reading of a wheel assembly, the temperature sensor of the thermal warning device should, preferably, extend deep into the wheel assembly. Unfortunately, the distance that a temperature sensor may extend into the wheel assembly varies with the type and configuration of the wheel assembly. Since existing thermal warning devices have temperature sensors with fixed lengths, it is costly for one to stock a variety of thermal warning devices, each having a different temperature sensor length. In addition, since existing thermal warning devices employ temperature sensors embedded in one of three wheel assembly retaining bolts, the bolt strength is degraded by the creation of a bore through the bolt. Additionally, bearings from different manufacturers operate at vastly different temperatures and precludes the use of a fixed threshold temperatures sensor. Further, a thermal warning device having a communication circuit that is positioned away from the wheel assembly tends to be expensive to manufacture and install.
Against the foregoing background, it is a primary object of the present invention to provide a thermal warning device having its electronic components positioned away from high temperatures of a wheel assembly in order to minimize the adverse effects caused by exposure to such high temperatures.
It is another object of the present invention to provide such a thermal warning device in which the body of the thermal warning device may be inserted into a threaded hole created on one side of the wheel assembly without mechanical degradation of the wheel assembly.
It is further object of the present invention to provide such a thermal warning device which includes a temperature sensor that extends deep into the areas near wheel assembly in order to obtain accurate readings of high temperatures in wheel assembly.
It is a still further object of the present invention to provide such a thermal warning device in which the temperature sensor is variable in length to adjust to the inner portion of the wheel assembly.
It is a still another object of the present invention to provide such a thermal warning device in which the electronic components of the thermal warning device are situated a particular distance away from the outer surface of the wheel assembly.
It is a still further object of the present invention to eliminate the need for drilling a bore into a support bolt of the wheel assembly.
It is a still further object of the present invention to eliminate the requirement of wheel shops or disassembly of the wheel assembly to replace old or damaged communication circuits.
It is a further object of the present invention optionally to include a radio transmitter, such as a spread spectrum transmitter, as means for communicating wireless signals from a variety of warning devices to respective receivers.
It is a yet another object of the present invention to provide such a thermal warning device that is inexpensive and simple to manufacture and install.
It is a still another object of the present invention to provide such a thermal warning device that has customized threshold temperature levels for different wheel assembly types and self-test diagnostic capability.